JPH05310431A - Iron alpha-oxyhydroxide and production of magnetic metal powder for magnetic recording using the compound - Google Patents

Abstract

PURPOSE:To provide a magnetic metal powder for magnetic recording having excellent aging stability and magnetic properties and to provide a process for producing the powder. CONSTITUTION:The process for producing this magnetic metal powder is composed of two steps consisting of (I) a step to add an aqueous solution of a ferrous salt, an aqueous solution of an aluminum salt and an aqueous solution of at least one kind of element selected from manganese, zinc, cobalt and calcium to a slurry of acicular iron alpha-oxyhydroxide, sufficiently mix the components by stirring, adjust the pH to <=2, oxidize with an oxidizing agent, heat to >=50 deg.C and neutralize and age the product at pH adjusted to >=3.5 with an alkali and (II) a step to wash the obtained slurry of iron alpha-oxyhydroxide having colloidal ferric hydroxide containing aluminum and at least one kind of element selected from manganese, zinc, cobalt and calcium uniformly applied to the surface of the particle, dry and calcine the slurry, reduce the product and form an oxidized layer on the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to .alpha.-iron oxyhydroxide and a method for producing magnetic metal powder for magnetic recording using the same.
Α-Iron oxyhydroxide uniformly coated with colloidal ferric hydroxide containing at least one of zinc, cobalt and calcium, and a fine magnetic powder using the same, which is excellent in stability and magnetic properties over time. The present invention relates to a method for producing a magnetic metal powder for recording.

[0002]

2. Description of the Related Art As a recent magnetic recording medium, a coating type magnetic recording medium using iron or a magnetic metal powder mainly containing iron has been put into practical use for the purpose of improving magnetic recording density and reproducing output.

Magnetic metal powders are usually α-FeOOH,
After acicular acicular iron oxyhydroxide (goethite) such as β-FeOOH and γ-FeOOH is dehydrated in an oxidizing gas atmosphere such as air into hematite while retaining its acicularity, it is treated like hydrogen. It is manufactured by a method of reducing to metallic iron under various reducing gas atmospheres. And the magnetic metal powder is
It is widely used as a magnetic recording medium such as a magnetic tape or a magnetic disk after being mixed with a binder resin to form a paint and then applied to a tape, a disk or the like.

However, although these magnetic metal powders have advantages such as a high recording density, they have a drawback that they are deteriorated over time as compared with the iron oxide magnetic powder.

Furthermore, with the recent trend toward higher recording densities, the magnetic metal powders are becoming finer, and the deterioration over time tends to decrease more and more.

In order to solve such problems, various proposals have been made to incorporate various elements such as aluminum into the magnetic metal powder (Japanese Patent Laid-Open Nos. 52-134858 and 62-65307). Japanese Patent Laid-Open No. 64-52
002, JP-A 64-33019, etc.).

However, in spite of these proposals, there is still a problem that deterioration with time is large.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems of the prior art. It significantly improves deterioration over time and has other required characteristics such as magnetic characteristics and paint dispersibility. To provide α-iron oxyhydroxide for obtaining a magnetic metal powder for magnetic recording, which can be maintained at a standard level and can sufficiently cope with miniaturization of the magnetic metal powder, and a method for producing the magnetic metal powder. is there.

[0009]

The above object of the present invention is achieved by the following method for producing α-iron oxyhydroxide and magnetic metal powder.

That is, the α-iron oxyhydroxide of the present invention has aluminum, manganese, zinc, cobalt,
Colloidal ferric hydroxide containing at least one of calcium is uniformly applied.

The method for producing magnetic metal powder for magnetic recording according to the present invention comprises: (I) a slurry of needle-shaped α-iron oxyhydroxide in a ferrous salt aqueous solution, an aluminum salt aqueous solution and manganese;
An aqueous solution of at least one salt of zinc, cobalt and calcium is added, thoroughly mixed and stirred, and after adjusting the pH to 2 or less, it is oxidized by an oxidizing agent and then heated to 50 ° C. or higher, and further pH is adjusted to 3 by alkali. Step of neutralizing and aging at 5 or more, (II) α obtained by uniformly depositing colloidal ferric hydroxide containing aluminum and at least one of manganese, zinc, cobalt and calcium on the obtained surface.
-After washing the iron oxyhydroxide slurry, drying and firing,
Then, a step of reducing in a reducing gas and further forming an oxide film on the surface is performed.

The manufacturing method of the present invention will be described in more detail below. In the present invention, needle-shaped α-iron oxyhydroxide is used as a raw material. The properties and production method of the acicular α-iron oxyhydroxide are not particularly limited, but the preferable average major axis diameter is 0.1 to 0.25 μm. Further, in addition to iron, it is desirable to contain at least one selected from nickel, manganese, aluminum, silicon, phosphorus, zinc, calcium and magnesium.

In the present invention, an aqueous solution of ferrous salt, an aqueous solution of aluminum salt and an aqueous solution of at least one salt of manganese, zinc, cobalt and calcium are added to the acicular α-iron oxyhydroxide slurry and mixed sufficiently. , Stir.

Examples of the ferrous salt used here include sulfates and chlorides, but sulfates are preferably used in consideration of economy and stability of the reaction.

As the aluminum salt, sulfate,
Examples include nitrates and chlorides. Also in this case, sulfate is preferable from the industrial point of view.

Further, as the salt of at least one of manganese, zinc, cobalt and calcium, sulfate, nitrate, chloride and the like are exemplified. Also in this case, sulfate is preferable from the industrial viewpoint.

The preferred range of the ferrous salt is 10/100 to 100/100 in terms of the atomic ratio of iron in the ferrous salt when the iron in the iron oxyhydroxide is 100. The preferred range of the aluminum salt is 1% iron in iron oxyhydroxide.
The atomic ratio of aluminum in the ferrous salt when set to 00 is 6/100 to 30/100. The salt of at least one of manganese, zinc, cobalt, and calcium is 0.1 / 100 to 10 / in terms of atomic ratio of manganese, zinc, etc. in the ferrous iron salt when the iron in iron oxyhydroxide is 100. 100.

In the present invention, it is necessary to adjust the pH of the iron oxyhydroxide slurry, which has been sufficiently mixed and stirred as described above, to 2 or less. For this, ferrous salt aqueous solution and aluminum salt aqueous solution and manganese, zinc, cobalt,
The acid may be added before or after the addition of the aqueous solution of at least one salt of calcium, in any case it is necessary that the pH of the iron oxyhydroxide slurry is adjusted to 2 or lower before the oxidation. If the pH exceeds 2, the ferrous salt in the slurry will newly form α-iron oxyhydroxide and magnetite.

Next, an oxidizing agent is added to this slurry.
The oxidizing agent used here is also not particularly limited, and may be any of air, oxygen, ozone, peroxide such as hydrogen peroxide solution, and the like. Peroxides such as hydrogen peroxide are particularly preferable. The reason for this is that particularly finely divided colloidal ferric hydroxide can be obtained by using a strong peroxide.

Next, the temperature of this slurry is raised to 50 ° C. or higher, preferably 70 ° C. or higher. If it is less than 50 ° C, fine aluminum and manganese on the surface in the subsequent neutralization aging step,
Colloidal ferric hydroxide containing at least one of zinc, cobalt and calcium is not uniformly applied, and as a result the properties and characteristics of the final magnetic metal powder are inferior. Then, this slurry is adjusted to pH 3.5 or more, preferably pH 3.5 to 9.0 with an alkali, and then heat-neutralized. The alkali used here is not particularly limited, but a carbonate such as sodium carbonate is generally used. Here, when the pH is less than 3.5, aluminum is not contained in the fine ferric hydroxide particles, and the properties and characteristics of the final magnetic metal powder are poor. Further, during neutralization and aging, a surface treatment of phosphorus and / or silicon may be performed to the extent that the dispersibility of the paint is not impaired. Thereby, the high temperature range can be used in the firing and reduction steps.

The α-iron oxyhydroxide in this slurry is
Colloidal ferric hydroxide containing fine aluminum and at least one of manganese, zinc, cobalt and calcium is uniformly applied to the surface thereof.

The slurry of α-iron oxyhydroxide thus obtained is washed, dried and fired. This drying is 1
The firing is performed at 00 to 200 ° C. for about 12 hours, and the firing is performed in the air or a nitrogen atmosphere at 300 to 800 ° C., preferably 400 to 700 ° C. Then, it is reduced in a reducing gas to further form an oxide film on the surface. This reduction is performed in a reducing gas such as hydrogen gas or carbon monoxide gas.
It is carried out at a temperature of 00 to 600 ° C., and is preferably 500 ° C. or higher in order to improve stability over time. Further, in order to form an oxide film on the surface, it is preferable to gradually increase the oxygen concentration in a mixed gas of an inert gas and oxygen gas and take out the magnetic metal powder finally obtained as the concentration in the atmosphere.

The shape of the magnetic metal powder for magnetic recording obtained by the production method of the present invention is needle-like, the average major axis diameter is preferably 0.05 to 0.25 μm, and the specific surface area is 4.
It is 0 to 55 m ² / g. The preferred composition is 1 iron.
In the atomic ratio of 00, aluminum is contained in an amount of 6 to 15 atom% and at least one of manganese, zinc, cobalt and calcium in an amount of 0.1 to 5 atom%.

[0024]

EXAMPLES The present invention will be specifically described below based on Examples and the like.

Example 1 100 g of needle-shaped α-iron oxyhydroxide having a specific surface area of 82 m ² / g and an average major axis diameter of 0.22 μm was well separated and suspended in 2000 ml of water.

Ferrous sulfate 0.80 mol / l was added to this suspension.
And 560 ml of a mixed aqueous solution containing 0.22 mol / l of aluminum sulfate and 0.03 mol / l of manganese sulfate were added, thoroughly mixed and stirred to disperse each component, and then the pH was adjusted to 1.7 at room temperature. ..

0.1 g of divalent iron ion was added to this slurry.
Hydrogen peroxide solution was added to oxidize until the amount became 1 / l or less. 1
After dispersing for an hour, the temperature was raised to 80 ° C., the pH was kept at 3.5 with an aqueous solution of sodium carbonate, and the mixture was thermally heated for 1 hour. Further pH
The temperature was maintained at 8 and the mixture was heated for 1 hour, then cooled and washed.

It was found that in the thus obtained α-iron oxyhydroxide, very fine colloidal ferric hydroxide was uniformly deposited on the surface of α-iron oxyhydroxide. As a result of chemical analysis, it was found that 100% of the added aluminum and manganese were deposited. That is, the deposited amount of aluminum was 11% in terms of atomic ratio when Fe in the starting material α-iron oxyhydroxide was 100.
Further, the amount of the ferric salt deposited was 41% in terms of atomic ratio when Fe in the starting material α-iron oxyhydroxide was 100. Further, the amount of manganese salt deposited is α- of the starting material.
The atomic ratio was 1.1% when Fe in iron oxyhydroxide was 100. The α-iron oxyhydroxide thus obtained has a specific surface area of 55 m ² / g and an average major axis diameter of 0.
It was 24 μm. The starting materials and manufacturing conditions are shown in Table 1.

The α-iron oxyhydroxide slurry was caked with a filter press and then dried at 100 to 120 ° C. overnight. Then, after firing in air at 600 ° C., reduction was performed in hydrogen gas at 550 ° C. to obtain acicular magnetic metal powder. Finally, a stable oxide film was formed on the reduced acicular magnetic metal powder and then taken out into the air to obtain a magnetic metal powder for magnetic recording.

As shown in Table 2, the properties were a specific surface area of 46 m ² / g and an average major axis diameter of 0.13 μm. Here, the specific surface area was measured by using a Micromeritics Model 2200 manufactured by Shimadzu Corporation, and the average major axis diameter was 100 which was recognized as a single particle on a TEM photograph.
The major axis diameter of each piece was measured, and the average value was obtained.

The magnetic characteristics of this magnetic metal powder were evaluated. The magnetic characteristics were measured for coercive force (Hc) and saturation magnetization (σs), using VSM manufactured by Toei Industry Co., Ltd. with an external magnetic field of 15 KOe and a packing rate of 1.20.

Further, in order to evaluate the stability over time, 60
The saturated magnetization amount (σs) after deterioration after leaving for 1 week in an atmosphere of 90 ° C. and 90% relative humidity was also measured. The results are shown together in Table 2.

Examples 2 to 15 Properties of acicular α-iron oxyhydroxide as a starting material, pH at oxidation, oxidizing agent, kind of salt of each element, addition amount of salt of each element, pH at aging .Alpha.-oxyhydroxide on which very fine colloidal ferric hydroxide was uniformly applied to the surface in exactly the same manner as in Example 1 except that the temperature during aging and the temperature during aging were changed as shown in Table 1, respectively. An iron slurry was obtained.

These α-iron oxyhydroxides were caked, dried, calcined and reduced according to Example 1 to obtain acicular magnetic metal powder. Finally, a stable oxide film was formed on the reduced acicular magnetic metal powder and then taken out into the air to obtain a magnetic metal powder for magnetic recording.

The properties and magnetic characteristics of this magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 1 As shown in Table 1, a slurry of α-iron oxyhydroxide was obtained in exactly the same manner as in Example 1 except that the oxidizing agent was not used and the ferrous salt was not added.

This α-iron oxyhydroxide was caked, dried, calcined and reduced according to Example 1 to obtain a needle-shaped magnetic metal powder. Finally, a stable oxide film was formed on the reduced acicular magnetic metal powder and then taken out into the air to obtain a magnetic metal powder for magnetic recording.

The properties and magnetic characteristics of this magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 2 A slurry of α-iron oxyhydroxide was obtained in exactly the same manner as in Example 1 except that aluminum salt was not added as shown in Table 1.

This α-iron oxyhydroxide was caked, dried, calcined and reduced according to Example 1 to obtain a needle-shaped magnetic metal powder. Finally, a stable oxide film was formed on the reduced acicular magnetic metal powder and then taken out into the air to obtain a magnetic metal powder for magnetic recording.

The properties and magnetic characteristics of this magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 3 As shown in Table 1, except that the pH during the oxidation reaction was set to 3,
A slurry of α-iron oxyhydroxide was obtained in exactly the same manner as in Example 1. Since magnetite was mixed in this slurry, the magnetic metal powder for magnetic recording could not be obtained.

Comparative Example 4 As shown in Table 1, a slurry of α-iron oxyhydroxide was obtained in exactly the same manner as in Example 1 except that the pH during aging was 3.

This α-iron oxyhydroxide was caked, dried, calcined and reduced according to Example 1 to obtain a needle-shaped magnetic metal powder. Finally, a stable oxide film was formed on the reduced acicular magnetic metal powder and then taken out into the air to obtain a magnetic metal powder for magnetic recording.

The properties and magnetic characteristics of this magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 5 As shown in Table 1, except that the temperature during aging was 30 ° C.,
A slurry of α-iron oxyhydroxide was obtained in exactly the same manner as in Example 1.

This α-iron oxyhydroxide was caked, dried, calcined and reduced according to Example 1 to obtain a needle-shaped magnetic metal powder. Finally, a stable oxide film was formed on the reduced acicular magnetic metal powder and then taken out into the air to obtain a magnetic metal powder for magnetic recording.

The properties and magnetic characteristics of this magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 6 As shown in Table 1, the pH during oxidation was 10, air was used as the oxidant, the pH during aging was 9.5, and the temperature during aging was 90 ° C. A slurry of α-iron oxyhydroxide was obtained by the same procedure as in 1.

This α-iron oxyhydroxide was caked, dried, calcined and reduced according to Example 1 to obtain a needle-shaped magnetic metal powder. Finally, a stable oxide film was formed on the reduced acicular magnetic metal powder and then taken out into the air to obtain a magnetic metal powder for magnetic recording.

The properties and magnetic characteristics of this magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 7 As shown in Table 1, a slurry of α-iron oxyhydroxide was obtained in exactly the same manner as in Example 1 except that at least one salt of manganese, zinc, cobalt and calcium was not added. It was

This α-iron oxyhydroxide was caked, dried, calcined and reduced according to Example 1 to obtain a needle-shaped magnetic metal powder. Finally, a stable oxide film was formed on the reduced acicular magnetic metal powder and then taken out into the air to obtain a magnetic metal powder for magnetic recording.

The properties and magnetic characteristics of this magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

[0055]

[Table 1]

[0056]

[Table 2]

As is clear from the results of Table 2, Example 1
Since Nos. 15 to 15 have higher saturation magnetization amounts in the initial stage and after deterioration as compared with Comparative Examples 1 to 2 and 4 to 7, it is understood that they have excellent magnetic properties and high stability over time. Further, by controlling the initial saturation magnetization amount in the oxide film forming step, it is possible to obtain an excellent deterioration rate (%). In Comparative Example 3, magnetite was generated, and thus was not a target for comparison.

[0058]

According to the present invention as described above, a fine magnetic metal powder for magnetic recording having excellent stability over time and magnetic properties can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadayoshi Saruwata 2-8-5 Hibi, Tamano City, Okayama Prefecture (72) Inventor Hisashige Ito 53-8 Uematsu, Nadasaki Town, Kojima District, Okayama Prefecture

Claims (2)

[Claims] 1. A surface containing aluminum, manganese, and zinc,
An α-iron oxyhydroxide, characterized in that colloidal ferric hydroxide containing at least one of cobalt and calcium is uniformly applied. 2. (I) A ferrous salt aqueous solution, an aluminum salt aqueous solution, and an aqueous solution of at least one salt of manganese, zinc, cobalt, and calcium are added to a slurry of needle-shaped α-iron oxyhydroxide, and the mixture is thoroughly added. After mixing and stirring, adjusting the pH to 2 or less, oxidizing with an oxidizing agent, then raising the temperature to 50 ° C. or more, and further neutralizing and aging at pH 3.5 or more with an alkali. And a slurry of α-iron oxyhydroxide uniformly coated with colloidal ferric hydroxide containing at least one of manganese, zinc, cobalt and calcium, washed, dried and fired, then in a reducing gas And a step of forming an oxide film on the surface of the magnetic powder for magnetic recording.